The present invention relates to a method of copy protecting an optical disc carrying content and control data arranged in physical sectors. The invention also relates to a method of copy protecting such an optical disc and to an instruction set for use in copy protecting an optical disc.
There are many techniques for copy protecting optical discs. For example, WO 00/74053 proposes copy protecting audio data on a digital audio compact disc (CD-DA) by rendering control data encoded onto the disc incorrect and/or inaccurate. The incorrect data encoded onto the CD is either inaccessible to, or not generally used by, a CD-DA player. Therefore a legitimate audio CD can be played normally on a compact disc music player, but the incorrect data renders the protected audio data on the CD unplayable by a CD-ROM drive.
As this earlier copy protection method prevents the user from using a CD-ROM drive legitimately simply to play the music or other audio on a CD-DA, alternative methods of copy protection have been proposed which, whilst preventing the production of usable copy discs, do not prevent or degrade the playing of legitimate optical discs on all players having the functionality to play such optical discs. Examples of such copy protection methods are described in WO 01/61695 and in WO 01/61696.
These further methods remove, corrupt, or otherwise render inaccurate control data associated with the information on the disc.
It has been found that there are many ways to deliberately subvert the content and/or the control data carried on an optical disc such that the disc cannot be reliably read or copied. However, there is a risk that the more effective the copy protection, the greater is the likelihood that the copy protection will adversely interfere with legitimate uses of the copy protected optical disc.